SIR – As a professor of atmospheric physics, at Imperial College London, I’m delighted that Boris Johnson maintains his interest in weather and climate (“It’s snowing, and it really feels like the start of a mini ice age”, Comment, January 21), but he should be wary of drawing generalised conclusions from his observations. He suggests that the cold weather is due to declining solar activity – but the sun is more active now than it has been since 2009, and about the same as it was in 2004 and 1998. What we have is the lovely variability of British weather sitting on top of a long-term global average warming due to greenhouse gas increases. This is not an issue of opinion, but one of basic physics.

So, Joanna compares the peak of extremely low current solar cycle 24 with the value half way up and down solar cycle 23.

I won’t be taking anything else she says seriously in future. It’s a nice demonstration of how you can mislead the public while being factually correct though.

As for “…warming due to greenhouse gas increases. This is not an issue of opinion, but one of basic physics.”

Joanna commits the same misleading error many cli-sci ‘experts’ before her have made and foisted on the public. That of taking the results of lab tests on the ‘basic physics’ of IR absorption and extrapolating it with no justification whatsoever to the real atmosphere where gases are not bounded by bell jars. The upper atmosphere has shrunk since 2003 when the sun went quiet, and the cloud deck is lowering. Evidence that natural variability is stronger than co2 forcing, and probably accounted for most if not all all the warming in the late C20th, as well as the cooling just begun.